1. Field of the Invention
The subject invention relates to a process for the preparation of cellular and non-cellular polyurethanes having desirable physical properties. More particularly, the invention relates to the preparation of cellular and non-cellular polyurethanes wherein selected polyetherpolyester polyols, prepared utilizing specific oxyalkylation catalysts, are utilized as the polyol component of the polyurethanes.
2. Description of the Prior Art
The preparation of cellular or non-cellular polyurethanes through the reaction of organic polyisocyanates with orgaic polyhydroxyl compounds (polyols) is well known. Particular attention is drawn, for example, to the monograph by J. H. Saunders and K. C. Frisch, High Polymers, Vol. XVI, "Polyurethanes," Pts. I and II (New York: Interscience Publishers, 1962, 1964) and by R. Vieweg and A. Hochtlen, Kunststoff-Handbuck, Vol. VII, Polyurethane, (Munich, Carl Hanser Verlag, 1966).
Ester group-containing polyether polyols are frequently used as the polyol component for the preparation of flame-resistant, semi-rigid, or rigid polyurethane foams. The preparation of these polyether-polyester polyols is illustrated by reference to U.S. Pat. Nos. 3,585,185, 3,639,541, and 3,639,542. For example, polyether polyols, which may contain phosphorus compounds as initiator molecules may be reacted with halogen-containing carboxylic acid anhydrides, in particular tetrabromo- or tetrachlorophthalic acid anhydride to form carboxylic acid half esters following which the free carboxylic acid groups are oxyalkylated.
According to European Patent Application 468, polyether polyol mixtures having a functionality of from 2.8 to 4.5 are reacted with tetrachlorophthalic acid anhydride in a hydroxyl-to-anhydride-group ratio of from 1:1 to 1.1:1 to form tetrachlorophthalic acid half esters and said half esters are then oxyalkylated with from 1 mole equivalent to 1.5 mole-equivalent of alkylene oxide. The resulting chlorine-containing polyether-polyester polyols are suitable for the preparation of rigid polyurethane or polyisocyanurate foams.
The oxyalkylation of reaction products prepared from carboxylic acid anhydrides and alcohols or amines in an equivalent ratio of from 0.1:1 to 2.0:1 with from 1.5 to 14 moles of alkylene oxide per mole equivalent of carboxylic acid anhydride is described in U.S. Pat. No. 3,445,886. These polyether-polyester polyols may also be utilized for the preparation of semi-rigid and rigid polyurethane foams.
The oxyalkylation described in the above references is generally performed in the presence of basic catalysts, for example, alkali hydroxides or alkali alcoholates, although occasionally acid catalysts is utilized. The disadvantage of these catalysts is that they not only accelerate the oxyalkylation of the carboxyl groups, they also catalyst polyoxyalkylation at the expense of complete initial esterification of the remaining acid functionality of the half esters. In order to assure that all the carboxy groups are completely esterified, the oxyalkylation must generally be performed with a large excess of alkylene oxide over a long reaction time. A further disadvantage is that the catalysts must be separated from the reaction mixture after completion of the reaction, which necessitates lengthy and expensive purification operations.
In order to avoid post-reaction purification, in European Application No. 468 and German Application No. 1 568 249, the oxyalkylation of the carboxylic acid half esters is performed in the absence of catalysts. However, a large excess of alkylene oxide is still necessary in the non-catalytic oxyalkylation in order to esterify all the carboxyl groups. A further disadvantage is that the non-reacted alkylene oxides, up to 15 weight percent of the amounts originally used, must be stripped. The stripping process, along with the need for proper disposal compromises the cost effectiveness and environmenal soundness of this process.
In order to eliminate this disadvantage, in German Pat. No. 3,201,203, the carboxylic acid half esters are oxyalkylated with one mole of alkylene oxide per mole-equivalent of carboxyl group, in the presence of a thiodialkylene glycol as a catalyst. In this process, particularly good results are obtained when glutaric acid anhydride is used to prepare the carboxylic acid half esters. However, if the polyols are reacted with other carboxylic acid anhydrides, such as tetrahydro- or phthalic acid anhydride, and the carboxylic acid half-esters are subsequently oxyalkylated, the resulting polyester or polyether-polyester polyols are difficult to process into polyurethanes in a reproducible manner. The process of the subject invention eliminates such defects by utilizing a process for the preparation of polyester or polyether-polyester polyols wherein the carboxylic acid half-esters are oxyalkylated in the presence of specific oxyalkylation catalysts.